The design of optimized optical telecommunications networks is a complex process of immense importance due to the high cost and constant evolution of system hardware and the impact of such design on localized and overall network performance. Key considerations in network design include the often conflicting needs to provide robust performance while simultaneously reducing costs of capital, operations and maintenance. Innovative optical network components, each with its own specific costs, capabilities and compatibilities, continue to become available for network implementation. Accordingly, a voluminous array of options must be considered in order to select components having optimal configurations for use at particular positions within a network, taking ongoing system demand changes into account. Among the multifaceted considerations to be addressed in system design are, for example, cost optimization, selection of equipment from a given subset of currently available components, the need to exploit the existing configurations of currently installed networks, and the need for least-cost routing of traffic that is entitled to varying levels of failure protection. Complex optimization systems that take into account all of these factors and others that may be applicable, are needed to aid network planners and service providers alike to design cheaper networks with the right equipment and network topology.
Core optical telecommunication networks commonly are nationwide systems. Sometimes such systems span entire continents. They mainly comprise two classes of network elements, namely, transmission and switching equipment. Transmission equipment comprises those elements that take care of the transport functionality of multiple wavelength light paths using dense wavelength division multiplexing (DWDM) transmission equipment. DWDM systems, also known as optical line systems (OLSs), comprise end-terminals where single wavelength optical signals are both regenerated upon exiting the OLS, and multiplexed into a single wavelength division multiplexed (WDM) signal upon entering the OLS. Hence the OLS facilitates the combined transmission of a plurality of telecommunication signals that are wavelength division multiplexed. Optical amplifiers are used to reamplify these OLS signals at periodic distances. After an optical signal has traversed a suitably long distance on a given optical fiber and has incurred a predetermined threshold attenuation, it is regenerated by first demultiplexing the signal into single wavelength signals, which then are reamplified. OLSs then feed the regenerated demultiplexed signals into optical cross-connects (OXCs) which switch the single wavelength traffic from a given input port to a desired output port that further feeds the optical signal into a wavelength division multiplexed OLS. Then the signal is combined with other signals into a WDM signal for further transmission toward its destination. Traffic demands are essentially fed on an appropriate pathway through both the core optical network and an underlying metro synchronous optical network (SONET), synchronous digital hierarchy (SDH) or Internet protocol (IP) network.
Optical add-drop multiplexers (OADMs) are a class of network components that can add or drop traffic when placed on an OLS. However, in contrast to OXCs, OADMs cannot perform switching. Thus, point to point traffic signals in a mesh network can either originate at an OADM or at a switching node containing an OXC. The introduction of OADMs thus necessitates determination of the optimal placement of OADMs and OXCs in a network.
Core optical networks are evolving towards a mesh architecture that supports multiple service level agreements (SLAs), including service that is entitled to failure protection and service that is not so protected. Much work has previously been done in mesh network design to address issues of routing traffic demands in terms of multiple wavelength light paths with varying failure protection schemes. Systems for network design and restoration of failed service have been presented, for example, to take care of 100% traffic restoration for a single point of failure in the network. See, for example, Optical Network Design and Restoration, Bharath T. Doshi et al, Bell Labs Technical Journal, Jan.-Mar, (4)1, 1999, which is hereby incorporated herein by reference in its entirety.
Core optical network design has also been extensively addressed in the literature. See, for example, SPIDER: A Simple and Flexible Tool for Design and Provisioning of Protected Lightpaths in Optical Networks, R. Drew Davis et al., Bell Labs Technical Journal, January-June, 2001 which is hereby incorporated herein by reference in its entirety. The SPIDER article describes an iterative system for routing traffic demands. Demands are routed on a least cost path, and an least cost topology is discovered once all the demands are routed in a given order. Each demand is then unrouted and re-routed until the cost of the network cannot be further reduced. This iterative heuristic system is used in routing demands with dedicated service failure protection, and in routing demands with no protection. Prior work on optical network design, routing, wavelength assignment and a general overview of optical networks is further described, for example, in Multi-wavelength Optical Networks: A Layered Approach, T. E. Stern et al, Addison-Wesley, (Reading, Mass. 1999), and Some Principles for Designing a Wide-Area Optical Network. B. Mukherjee et al, IEEE Conference on Computer Communication (INFOCOM 94), June, 1994 both of which are hereby incorporated herein by reference in their entirety.
All of these known systems, however, assume the presence of an OXC at all nodes in the network. Given the overlapping and varying capabilities and costs of OADMs and OXCs, there is a need for a system to determine the optimal placement of OADMs and OXCs in a mesh network satisfying multiple service restoration schemes, only some of which may be entitled to failure protection. In addition, there is a need for systems that are capable of determining the optimal configuration and size of OXCs across such a mesh network. A key motivation for addressing these needs is the fact that OADMs are significantly less expensive than OXCs, and accordingly it is preferable to place as many OADMs as possible in a given mesh network.